Sleeve supported electrode fob



Feb. 24, 1953 A. B. HILDEBRANDT 23,521

SLEEVE SUPPORTED ELECTRODE FOR WELL LOGGING Original Filed Sept. 21,1949 5 Sheets-Sheet 1 F I C, i

Glexarzder 5. Hildebrarldi Jnventor 'Clbbori'zes Feb. 24, 1953 A. B.HILDEBRANDT 23,521

' SLEEVE SUPPORTED ELECTRODE FOR WELL LOGGING 5 Sheets-Sheet 2 OriginalFiled Sept. 21, 1949 Cllexarider b. HildebrandtCSrzvenbor A. B.HILDEBRANDT SLEEVE SUPPORTED ELECTRODE FOR WELL LOGGING I Feb. 24, 1953s Sheets-Shet 5 Original Filed Sept. 21, 1949 ClZea cancler b.Hzlldebrandt {Inventor 238w- Clbbol neg I Feb. 24, 1953 A. B.HILDEBRANDT Re. 23,621

SLEEVE SUPPORTED ELECTRODE FOR WELL LOGGING Original Filed Sept. 21-,1949 SSheets-Sheet 4 6i 52 52 s4 s5 50 FLQ-JO G Lcxarzder 6b- HLLdcbrandt -{n.ver1bor $5 5 111 (2 Cbborneg Feb. 24, 1953 A. B.HILDEBRANDT Re. 23,621

sLEEvE SUPPORTED ELECTRODE FOR WELL LOGGING 5 Sheets-Sheet 5 OriginalFiled Sept. 21, 1949 Cltb orneg bg w Rama-m. :4; 953 a Re. 23,621 UNITEDSTATES; PATENT OFFICE sum surroa'ran anac'raona roa WELL LoGGmoAlexander B. Hildebrandt, Tulsa, Okla, alsignor to Standard OilDevelopment Company. a corporation of Delaware Original No. 2,552,428,dated May 8, 1951, Serial No. 117,058, September 21, 1949. Applicationfor reissue September 26, 1952, Serial No.

2; Claims. (01. 175-182) Hatter enclosed in heavy when l: 1 appears inthe ii -mun patent but forms no part of unrel-lie specification: matterprinted in italics indicates the additions made by reissue.

This invention. is concerned with apparatus for the electrical loggingof bore-holes in the' earth. such as oil wells; and more particularlywith an improved type of electrode for use in electrical 1088 8 .todetermine the nature of strataencountered by a bore hole.

. Methods and apparatus for the logging of bore holes by measuringimpedance self potentials, resistance or-some other electrical propertyof the' various strata through whichthe bore hole well known. Some ofthese are de- -,-scribed'for example in the Schlumberger patents suchas. 1,819,923; 1,894,328; 1,913,293 and 2,165,013. 'These methodsinvolve the lowering of one or more electrodes into a bore hole filledwith.water or with aqueous drilling mud, sending "currents into theformation and observing the electrical phenomena produced.

One of the more common procedures is to mak electrical measurementsindicative ofthe diiference in apparent resistivity of the various typesof rocks encountered as the. electrodes are raised up throughthe borehole. A particular dimculty arising in suclimeasurements, however, isthat the resistivity of the mud or water in .the bore hole enters intothe measurement and in some .lnstances causes anomalous or misleadingresults, as will beexplained more fully hereinafter.

It is one object of the present invention to provide an electrodeassembly for electrical well loggin which will eliminate or minimize thesources of error in conventional methods of electric logging of boreholes. Another object of the invention is to provide well loggingelectrodes which will besubstantialiy shielded electrically -from themud column in a well and thus substantially eliminate erroneous well loging readings. Other and further objects and advantages of this inventionwill be apparent from the ensuing description taken in conjunction withthe accompanying drawing in which Fig. 1 is a vertical cross sectionalview of a section of a bore hole together with the conventionalapparatus placed therein and on the earths surface for making anelectric log of the bore hole and illustrating particularly thedisadvantage of theconventional well loggin Procedure.

2 show the assembly in its operating or open position for traveling upthe bore hole and making an electric log thereof;

Fig. 6 is a cross sectional view along line A-li' of Fig. 2;

Fig. '7 is a detailed view of the lower end of the mechanism of Fig. 3,showing particularly the sleeve fastening means;

Fig. 8 is a cross, sectional view taken along line 13-13 of Fig. 4;

Fig. 9 is a crow sectional view taken along lineC-CofI ig.8;and,

Fig. 10 is a view of a typical record obtained in a modification of thedevice of this invention to enable the determination of dip and strikeof strata encountered.

Referring to the drawing in detail and in particular to Fig. '1 thereof,reference numeral I denotesa bore hole filled with drilling mud 2 andinto which is suspended a cable 3 carrying a plurality of conductors l,I, 6,,each having an electrode I, I, 9. The cable is supported over thebore hole on a pulley Iii and is wound onto a reel II. By suitablecollector rings l2, electrical contact is made between conductors ta,5a, 8a and the corresponding conductors l, 5 and 8 in cable 2.-Conductor la is connected to one terminal of potential source I, theother end of which is connected to ground. Surface casing ll maysuitably serve as the ground electrode,

Conductors Ia and 6a connect into a recording potentiometer or similarrecording device it provided with means for feeding a roll of paper pasta recording stylus or the like in proportion to the length of cablebeing wound on reel ll. Means for measuring the length of cable in thebore hole and the tension on the cable, and for Figs. 2 and 3 arevertical cross sectional views .of a bore hole' with the electrodeassembly of the present invention suspended therein, the assembly beingdepicted in cross section in its initial or closed condition forlowering into the bore hole, Fig. 3 representing a lower continuation ofFig. 2:

Figs! and'ii co nd to Figs. 2 and 3 and relating the recording papermovement to the movement of the cable, are not depicted here,

as these devices are conventional and their description is not pertinentto the discussion of the present invention.

The theory of formation resistivity measurements is fully explained inthe aforementioned Schlumberger patent, 1,819,923 and is briefly asfollows: Current enters the ground through electrode I and flows to theground electrode, i. e. the surface casing it. The flow of electricalcurrent is represented by lines 0. Now if the distances from electrode 1to electrode 8 and from electrode 1 to electrode 9 are relatively largewith respect to the diameter of the bore hole,

say 10 to 20 times saiddiameter, there will be created a difference inpotential between electrode I and I, which'can be measured withrepointed out by 'Schlumberger, that the current flowing from'electrode1 produces by ohmic effect equipotential surfaces which are essentiallyspherical surfaces centered on electrode 1. It

' is assumed that since the cross sectional area of the bore hole issmall compared to the distances fromelectrode 1 to electrodes '8 and 9there is no appreciable deformation of the spheres by the column ofwater or drilling mud in the bore hole. so that the measure of potentialbetween electrodes 3 and 9 is eouivalent to a measure of the differencein potential in the adjacent formation at equivalent distances fromelectrode 1.

The res stivity measured b the above method is approximately the realresistivity only if it is assumed that the formations in the vicinity ofthe electrodes 1, 3 and 9 are homo eneous and .that the effect of the cou n of mud or water is negligible. Fuch is not the case, however. and inact al pract ce what is measured is not t e real resistivitv but what iscalled ap arent resistivitv. influenced b b th the resist vity of thedrilling mud and the different types of rocks encountered. Nevertheless,rock lavers having differences in resistivltv are detected withreasonable accuracy by means of the usual apparent resistivitymeasurements. However, when it is desired to obtain indication betweendifferent layers with a high de ree of definition. especially when thelavers are relatively thin. the resistivity of the drilling mud or waterrelative to the re sistivity of the formation levers enters into thepicture. For exam le, if a thin bed I! of high resistivity isencountered, its presence may not show up on the record, because of theshort circuiting of current through the drilling mud from electrode 9 toelectrode 9, giving a resistivity reading which will be lower than wouldbe obtained if the resistivity through layer l9 were the only factor.

Reference will now be made to the remaining figures of the drawing,showing the features of the present invention. Referring particularly toFigs. 2 and 3, a case 2| is suspended by cable 3 in a bore hole I fllledwith drilling mud 2. Pivotally attached to the lower end of case 2| area plurality of arms 25. A centrally disposed elongated rod member 26 isscrewed into base 66 in case 2|. Slidably fitted over rod 26 is arotatable sleeve 21 provided at its lower end with curved pins 29adapted to engage holes 29 at the lower ends of arms 25 and to releasesaid arms upon rotation of sleeve 21. This is shown in detail in Fig. 6,which is a cross-sectional view along line A-A of Fig. 2. The mechanismfor rotating sleeve 21 to release arms 25 is contained in case 2| andwill be described in more detail later in the specification.

Attached to the lower end of the arms 25 is a flexible, open, elongated,rubberized sleeve 39 extending for almost the full length of rod 26 asshown in Fig. 3. Sleeve 39 is yieldably fastened at its lower end to rod26 by fastening means 3|. Embedded in the wall of sleeve 39 are aplurality of sets of electrodes, 33, 36, an of the electrodes 33 beingelectrically connected and all ofthe electrodes 36 being electricallyconnected. Insulated leads 31 and 3B embedded in sleeve 39 con-Depending upon the particular use that is to be made of the device, onlya single set oi electrodes such as 33 might be utilized or both sets 33and 36 might be employed. In the preferred embodiment of the inventionboth sets are employed and in addition rod 26 is an insulated rod on thelower end of which is fitted an additional electrode which is connectedelectrically to surface equipment by means of lead 6| running up throughrod 26, case 2 I and cable 3. Thus electrodes 69, 33 and 36 correspondin their function to electrodes I, 8 and 9 of Fig. l.

The apparatus of the invention is depicted in its non-logging positionin' Figs. 2 and 3 and in this position is adapted to be lowered into thewell to be logged. When the desired depth has been reached the trippingmechanism contained within case 2| rotates sleeve 21, releasing pins 28from engagement with holes 23, thereby permitting arms 25 to moveoutwardly because of the tension exerted by springs 23, which areattached to the ends of arms 25 and to bracket 58. Since the arms 25move independently of each other, each will move outwardly until ittouches the walls of the bore hole, causing the upper rim of flexiblesleeve 39 to conform to the cross section of the bore hole walls Inother words, substantially the entire upper or leading edge of thesleeve will be brought into contact with the periphery of the bore hole.As the assembly moves up the bore hole, drilling mud 2 will enter sleeve39 and cause [it] the sleeve to contact the bore hole wall, thusbringing electrodes 33 and 36 into contact with the wall of the borehole. As drilling mud reaches the bottom of the sleeve 39, thedifferential pressure resulting from upward motion of the sleeve willcause the lower end of the sleeve to pull free from holding means 3|,thus allowing substantially all ofthe drilling mud to be bypassedthrough sleeve 39 at the device moves upwardly through the bore hole.Potential measurements are made in the conventional manner withelectrodes 33 and 36, using a current introduced by electrode 69.

Details of the holding means 3| and the manner in which it functions areillustrated in Fig. '7. Holding means 3| comprises a semi-rigid materialsuch as heavy rubber or rubber-impregnated fabric which is tightly boundto rod 26 by means of wire or similar material 32. The wall thickness ofmeans 3| is considerably [thicker] greater at its uppermost portion inorder to form a rim 3|a which will hold the lower end of the sleeve 39against rod 26. The wall of holding means 3| is sufilciently flexible sothat as suiii cient mud pressure is built up inside the sleeve the lowerend of the sleeve will be permitted to slide past rim 3 a.

To ensure that the upper or leading edge of open flexible sleeve 39 willfollow the contour of bore hole I as the device is raised up through thebore hole, arms 25 are provided with shorter arms 26 which are pivotallfastened to arms 25 by means of pins 22. The short arms 26 are of flatcross-section as illustrated in Fig. 9, which is a cross-section takenalong line 0-0 of Fig. 8. The ends of the short arms 26 are fastened tosleeve 39 at intermediate points between the ends similar material toensure maximum flexibility in following the contour of the hole.

The mechanism for releasing arms 2! is also depicted in Figs. 2 and 4.Rotatable sleeve 21- is supported by bearings 42 and 43 and has attachedto its upper end a gear 45 which meshes with a spur gear 46 attached torotatable shaft I, supported on bearings 49 and II. A lever 52 extendingat right angles to the axis of shaft 41 is secured to the shaft justabove base 44. Spring ll, wound about shaft 41, has its upper endattached to support member 59 and its lower end secured to lever 52, sothat spring 5| exerts a bias on shaft 41 in the clockwise direction,viewing shaft 41 from its lower end. A Jointed bar ii is provided, beingconstructed with arms BI and 84 secured together by a pin -58. Arm ll issecured to lever arm 52 of shaft II by pin 58 and arm 54 is secured to aportion of case II by pin 51.

The means for actuating the releasing mechanism consists of an armature62 having a vertical axis and slidably arranged in a coil of wire 83. Anelectric current can be sent through coil 83 through leads 64 and 65which run to the surface equipment through cable 3. Passage of such acurrent through coil 63 will cause armature 62 to be drawn upwardly sothat it strikes the center of bar 60. The resulting movement of pivot 65of jointed bar 60 above the line joining pivots 56 and 51 causes the barto buckle because of the bias exerted by spring 5|, thus causing shaft41 to rotate through an angle of about 90. Gear 48 likewise rotatesthrough the same angle and causes gear 45 and sleeve 21 to rotate in theopposite direction through a sufficient angle to disengage pins 28 andholes I! in the lower ends of arms 25, the gear ratio; between gears 45and 46 being so selected that the pins II will be pulled clear of arms25.

The advantages of the present invention will be readily apparent tothose skilled in the art of electric logging of wells. Since theelectrodes 33 and N are in substantial contact with the walls of thebore hole at all times and are insulated from the main column of mud,the resistivity readings obtained will not be, seriously affected byvariations in hole size nor by mud in the hole. It is anticipated thatsleeve 30 will not completely prevent mud from passing between thesleeve and the walls of the bore but nevertheless the amount of mudremaining in this vicinity will be so small and of such narrow crosssection that its resistivity will be high, compared to that of theadjacent formation, so that the mud resistivity will be a negligiblefactor in the measurement. Since the sleeve can accommodate a largevolume of drilling mud, the device will meet but little resistance onits way up the bore hole, thus permitting a rapid log of the bore holeto be made.

It is obvious that modification of the assembly described can be madewithout departing from the scope and spirit of the invention. Forexample by using three or four electrodes in each of the groups I3 and34 and spacing the electrodes in each group uniformly in a horizontalplane about the circumference of sleeve 30 and providing separateelectrical leads 31 and 38 from each individual electrode to surfaceinstruments it is possible to obtain measurements that will beindicative of the dip and strike of strata encountered. Assume that fourelectrodes are used in each group and that they are designated as Ila,"b, He. 33d, a, etc., 33a and 34a as shown in Fig. 9, 8| being the traceof the potentia] measured from electrodes 33a and 34a,

82 for electrodes 33b and 34b, and so on. A fifth trace, 85 may be madeto show the orientation of one of the electrodes, say 33a with respectto North on the compass by providing wthin case 2i in the bore hole asuitable orienting apparatus, such as that described and claimed in theBoucher patent, 2,332,777, and tracing the impulses on moving paper 80simultaneously with the other traces Ola, etc. A sixth trace 86 maydesignate the depth of the instrument at any time on the record by meanswell known in the art, or the depth may be recorded manually on thechart from readings of suitable depth measuring instruments.

Assume further, for the purpose of simplifying the explanation, thatmeasurements on trace 85 indicate, by the method outlined in theaforementioned Boucher patent, that electrodes 33a and 34a are orientedNorth; then electrodes 33b and 34b will lie East, 330 and 340 South, and33d and 34d West. With paper 80 moving in the direction indicated by thearrow, peaks 8! on traces BI, 82, etc. show that a stratum of differentresistivity was encountered first by North electrodes 33a and 34a, thenby East and West electrodes 33b, 34b, 33d, and 34d and finally by Southelectrodes 33c and 340. This indicates that this particular stratum dipsin a northerly direction.

It is not intended that the invention be restricted to the specificembodiments described, which have been presented merely by way ofexample. The invention is to be limited only by the following claims.

What is claimed is:

[1. An electrode assembly for the electric logging of bore holescomprising an elongated flexible insulat ng sleeve adapted to contactsubstantially the entire periphery of the bore hole, at least oneelectrode carried by said sleeve in a section intermediate its ends,said electrode being insulated from the interior of ,said sleeve butelectrically accessible from the exterior of said sleeve, and means forsupporting said sleeve in said bore hole and for pressing its upperperiphery into contact with the periphery of the bore hole] [2. Anelectrode assembly according to claim 1 in which an additional electrodeis supported adjacent the lower end of said sleeve on insulatedsupporting means disposed within said sleeve] 3. An electrode assemblyfor the electric logging or bore holes comprising a supporting bodyadapted to besuspended within said bore hole on a cable, a plurality ofarms pivotally attached to the lower portion of said body, each armbeing adapted for independent movement outwardly from said body, meansurging each of said arms outwardly from said body, an elongated flexibleinsulating sleeve attached at its upper end to the lower extremities ofsaid arms, and at least one electrode carried by said sleeve in asection intermediate its. ends, said electrode being insulated fromt heinterior of said sleeve but electrically accessible from the exterior ofsaid sleeve.

4. Electrode assembly according to claim 3 in oi the flexible sleeve.

I which a plurality ot electrically connected electrodes are carried bysaid sleeve about a horiaontal periphery thereof.

5. Electrode assembly according to claim 3 in which said sleeve carriesat least two groups of electrodes, the electrodes in each group beingelectrically connected to each other and dispos about a horizontalperiphery of said sleeve, the electrode groups-being placed in verticalrelation to each other in a section intermediate the ends 8. Electrodeassembly according to which an additional electrode is supportedadjacent the lower end of said sleeve on an insulated supporting meansdisposed within said sleeve and attached to said supporting body.

7. An electrode assembly for the electric loggins oi bore holescomprising a supporting body adapted to be suspended within said borehole on a cable, a plurality of arms pivotally attached claim 3 in tothe lower portion of said body, spring means independently urging each01' said arms outward- 1y from said body, releasable locking means forholding said arms inwardly in opposition to said spring means,electrically operable I releasing means for said locking means, anelongated-flexible insulating sleeve attached at its upper edge to thelower extremities of said arms. an elongated rod attached at its upperend to said supsaid electrode being insulated from the interior l a ofsaid sleeve but electrically accessible from the exterior of saidsleeve. I

8. Electrode assembly according to claim 7 in which said elongated rodis an insulated rod and in which an additional electrode is supported bythe lower end of said insulated rod.

9. An electrode assembly for the electric logplay of bore holescomprising an open elongated flexible insulating sleeve adapted tocontact substantially the entire periphery of the bore hole, at leastone electrode carried by said sleeve in a section intermediate its ends,said electrode being insulated from the interior of said sleeve butelectrically accessible from the exterior of said sleeve, means forsupporting said sleeve in said bore hole and means {or pressingsubstantially the entire upper edge of said sleeve into contact with theperiphery ofthe bore hole, whereby substantially all of the fluid in thebore hole in the vicinity of,

the sleeve will pass through said sleeve as said sleeve is raisedthrough the bore hole by said supporting means.

10. An electrode assembly according to claim 9,

including insulated supporting means disposed within said sleeve and anadditional electrode supported ada'aeent the lower end of said sleeve onsaid insulated supporting means.

' ALEXANDER. B. HILDEBRANDT.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS

